PREDICTING PATTERNS OF PREY USE FROM MORPHOLOGY OF FISHES

Ecomorphological analyses that search for patterns of association betw een morphological and prey-use data sets will have a greater chance of understanding the causal relationships between form and diet if the m orphological variables used have known consequences for feeding perfor mance. We explore the utility of fish body size, mouth gape and jaw-le ver mechanics in predicting patterns of prey use in two very different communities of fishes, Caribbean coral reef fishes, and species of th e Centrarchidae that live in Lake Opinicon, Ontario. In spite of major differences in the spectrum of potential prey available, the centrarc hids of Lake Opinicon show dietary transitions during ontogeny that ar e very similar to those seen among and within species of Caribbean gro upers (Serranidae). The transition from small zooplankton to intermedi ate sized invertebrates and ultimately to fishes appears to be very ge neral in ram-suction feeding fishes and is probably driven largely by the constraints of mouth size on prey capture ability. The jaw-lever s ystems for mouth opening and closing represent direct trade-offs for s peed and force of jaw movement. The ratio of in-lever to out-lever in the opening system changes during ontogeny in bluegill, indicating tha t the mechanics and kinematics of jaw movement may change as well. Amo ng 34 species of Caribbean reef fishes, biting species had jaw-closing ratios that favored force translation, while species that employ rapi d-strike ram-suction had closing ratios that enhanced speed of closing and mouth opening ratios that favored a more rapid expansion of the m outh during the strike. We suggest that when prey are categorized into functional groups, reflecting the specific performance features that are important in capturing and handling them, and the differences amon g habitats in the available prey resource are taken into account, gene ral patterns can be found in morphology-diet relations that cross phyl ogenetic boundaries.